The establishment of dense nesting cover (DNC) for breeding waterfowl is a common management practice on large blocks of former agricultural land. The Delta Waterfowl Foundation\u27s Adopt-A-Pothole (AAP) program establishes DNC adjacent to small wetland complexes to increase waterfowl use and productivity. I evaluated waterfowl use and nesting success on AAP lease sites in southwestern Manitoba in 993- 94 and compared the relative amount and success of overwater and upland nesting by mallards using these sites.
Diving duck breeding pair densities were higher on treatment sites in both 1993 and 1994 (P= 0.02 and 0.02, respectively). Dabbling duck breeding pair densities did not differ between sites. Upland nesting success did not differ between control and treatment sites in 1993 (P = 0.16) and was higher on control sites in 1994 (P= 0.02). Overwater nesting success did not differ between treatment and control sites in 1993 or 1994 (P = 0.66 and 0.08, respectively). Brood use was difficult to quantify because of high water levels in both years.
Overwater nests comprised 31% (n = 58) of the total mallard (Anas platyrhynchos) nests found in 1993-94. Mallard overwater and upland nest success was not different (P = 0.39). Mallards nested in shallower water than ruddy ducks (Oxyura jamaicensis), canvasback (Aythya valisineria), and redhead (A. americana) (P \u3c 0.0005). Mallards nested closer to shore than redheads (P = 0.02). Ruddy duck and canvasback daily survival rates were highest, followed by redhead and mallard (P = 0.06 to 0.18). Overwater nests located in \u3c 30 cm of water were predated more often than expected (P \u3c 0.0025).
Deeper water may provide greater security from predators for overwater nesting ducks than shallower water. The importance of overwater nesting by mallards probably varies regionally and annually. Wetlands, primarily seasonal and semi-permanent, appear to provide attractive mallard nesting habitat. The establishment of DNC adjacent to small wetland complexes located in agriculturally dominated landscapes may provide relatively secure and attractive waterfowl nesting habitat. However, other factors, including the presence and abundance of potential nest predators, may influence the effectiveness of this practice
